Oxynitride compounds, methods of preparation, and uses thereof

ABSTRACT

Embodiments of the present disclosure provide for methods of transforming from one crystal structure to another crystal structure in TiO 2  nanocolloids and TiO 2-x N x  nanocolloids.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to copending U.S. ProvisionalApplication entitled, “Conversion of Anatase to Rutile TiO₂ at RoomTemperature Using Transition Metal Ion Based Seed Compounds”, filed withthe United States Patent and Trademark Office on May 12, 2005, andassigned Ser. No. 60/680,412, which is entirely incorporated herein byreference.

This application claims priority to and is a continuation-in-part ofU.S. Utility Patent Application entitled, “Oxynitride Compounds, Methodsof Preparation, and Uses Thereof”, filed with the United States Patentand Trademark Office on Dec. 20, 2002, and assigned Ser. No. 10/324,482,U.S. Pat. No. 7,071,139, which claims priority to copending U.S.Provisional Application entitled, “Generation of TiO_(2-x)N_(n)Photocatalysts from the Solution Phase Nitration of TiO₂”, filed withthe United States Patent and Trademark Office on Dec. 21, 2001, andassigned Ser. No. 60/342,947, both of which are entirely incorporatedherein by reference. In addition, this application claims priority toand is a continuation-in-part of U.S. Utility Patent Applicationentitled, “Oxynitride Compounds, Methods of Preparation, and UsesThereof”, filed with the United States Patent and Trademark Office onMar. 9, 2006, and assigned Ser. No. 11/371,788, U.S. Pat. No. 7,186,392,which claims priority to and is a divisional application of U.S. UtilityPatent Application entitled, “Oxynitride Compounds, Methods ofPreparation, and Uses Thereof”, filed with the United States Patent andTrademark Office on Dec. 20, 2002, and assigned Ser. No. 10/324,482,U.S. Pat. No. 7,071,139, which claims priority to copending U.S.Provisional Application entitled, “Generation of TiO_(2-x)N_(x)Photocatalysts from the Solution Phase Nitration of TiO₂”, filed withthe United States Patent and Trademark Office on Dec. 21, 2001, andassigned Ser. No. 60/342,947, all of which are entirely incorporatedherein by reference

TECHNICAL FIELD

The present disclosure is generally related to oxide compounds and, moreparticularly, is related to oxynitride compounds and methods ofpreparation thereof.

BACKGROUND

The initial observation of the photoinduced decomposition of water ontitanium dioxide (TiO₂) has promoted considerable interest in solarcells and the semiconductor-based photocatalytic decomposition of waterand of other organic materials in polluted water and air. A continuedfocus on TiO₂ has resulted because of its relatively high reactivity andchemical stability under ultraviolet excitation (wavelength <387nanometers), where this energy exceeds the bandgaps of both anatase (3.2eV) and rutile (3.0 eV) crystalline n-TiO₂.

However, both anatase and rutile TiO₂ crystals are poor absorbers in thevisible region (wavelength <380 nm), and the cost and accessibility ofultraviolet photons make it desirable to develop photocatalysts that arehighly reactive under visible light excitation, utilizing the solarspectrum or even interior room lighting.

With this focus, several attempts have been made to lower the bandgapenergy of crystalline TiO₂ by transition metal doping and hydrogenreduction. One approach has been to dope transition metals into TiO₂ andanother has been to form reduced TiO_(x) photocatalysts. However, dopedmaterials suffer from a thermal instability, an increase ofcarrier-recombination centers, or the requirement of an expensiveion-implantation facility. Reducing TiO₂ introduces localized oxygenvacancy states below the conduction band minimum of titanium dioxide sothat the energy levels of the optically excited electrons will be lowerthan the redox potential of the hydrogen evolution, and the electronmobility in the bulk region will be small because of the localization.

Films and powders of titanium oxynitride (TiO_(2-x)N_(x)) have revealedan improvement over titanium dioxide under visible light in opticalabsorption and photocatalytic activity, such as photodegradation ofmethylene blue and gaseous acetaldehyde and hydrophilicity of the filmsurface. Substitutional doping of nitrogen by sputtering a titaniumdioxide target in a nitrogen/argon gas mixture has been accomplished.After being annealed at 550° C. in nitrogen gas for four hours, thefilms were crystalline with features assignable to a mixed structure ofthe anatase and rutile crystalline phases. The films were yellowish incolor, and their optical absorption spectra showed them to absorb lightbetween 400-500 nm, whereas films of pure titanium dioxide did not.Photocalytic activity for the decomposition of methylene blue showsactivity of TiO_(2-x)N_(x) at wavelengths less than 500 nm.

The active wavelength of TiO_(2-x)N_(x) of less than 500 nm promises awide range of applications, as it covers the main peak of the solarirradiation energy beyond Earth's atmosphere. Further, it is anexcellent light source, peaking at 390 to 420 nm, provided byrecently-developed light-emitting indium gallium nitride diodes.

In addition, nitrogen can be incorporated into the TiO₂ structure by thenitridation reaction of TiO₂ nanopowders that are subjected to anammonia (NH₃) gas flow at about 600° C. Transmission electron microscopemicrographs showed that the synthesized TiN powder consisted of uniformspherical particles with an average diameter of about 20 nm whennitridation was performed at a temperature of about 600° C. for 2-5hours. No results with respect to the photocatalytic activity of thismaterial were presented.

The synthesis of chemically modified n-type TiO₂ by the controlledcombustion of Ti metal in a natural gas flame at a temperature of about850° C. represented another attempt at lowering the band gap energy ofTiO₂. The modified films were dark gray, porous in structure and with anaverage composition of n-TiO_(2-x)C_(x) (with x about 0. 15). Thismaterial absorbs light at wavelengths below 535 nm and has a lowerband-gap energy than rutile TiO₂ (2.32 versus 3.00 electron volts). Whenilluminated with a 150 Watt xenon (Xe) lamp, and at an applied potentialof 0.3 volt, the chemically modified n-TiO_(2-x)C_(x) (with x about0.15) exhibited a higher water photoconversion efficienty (8.3%) thanthat of pure TiO₂ illuminated under the same conditions (1%).

All of these examples require the use of very high temperature synthesisconditions, and long periods of time to produce these materials. Thetime and temperature previously required to make the TiO_(2-x)N_(x) andn-TiO_(2-x)C_(x) compounds makes these techniques costly andinefficient.

Thus, a heretofore unaddressed need exists in the industry for a simplemore cost effective method to fabricate novel materials capable ofexhibiting photo catalytic activity such as the photo-induceddecomposition of water and pollutants. Additionally, a need exists forbetter methods for their use in the production of electricity throughsolar cells, as well as to address some of the aforementioneddeficiencies and/or inadequacies.

SUMMARY

Embodiments of the present disclosure provide for methods oftransforming from one crystal structure to another crystal structure inTiO₂ nanocolloids and TiO_(2-x)N_(x) nanocolloids. One representativeembodiment includes: providing a TiO₂ nanocolloid that has an anatasecrystal structure; mixing the TiO₂ nanocolloid with a metal hydratecompound at a temperature of less than about 600° C., wherein the metalhydrate compound is selected from a cobalt chloride hexahydratecompound, a cobalt nitrate hexahydrate compound, and a nickel chloridehexahydrate compound; and transforming the anatase crystal structure toa rutile crystal structure in less than 60 minutes and at a temperatureof less than about 600° C.

Another embodiment of the present disclosure provides for methods oftransforming from one crystal structure to another crystal structure. Anexemplary method includes: providing a TiO₂ nanocolloid that has ananatase crystal structure; mixing the TiO₂ nanocolloid with a metalhydrate compound at a temperature of about 20 to 30° C.; andtransforming the anatase crystal structure to a rutile crystal structurein less than 5 minutes and at a temperature of about 20 to 30° C.

Another embodiment of the present disclosure provides for methods oftransforming from one crystal structure to another crystal structure. Anexemplary method includes: providing a TiO_(2-x)N_(x) nanocolloid thathas an anatase crystal structure, wherein x is about 0.005 to 0.25;mixing the TiO_(2-x)N_(x) nanocolloid with a metal hydrate compound at atemperature of less than about 600° C., wherein the metal hydratecompound is selected from a cobalt chloride hexahydrate compound, acobalt nitrate hexahydrate compound, and a nickel chloride hexahydratecompound; irradiating the interaction of the mixture of theTiO_(2-x)N_(x) nanocolloid and the metal hexahydrate compound with alaser energy of greater than 120 mW; and transforming the anatasecrystal structure to a rutile crystal structure.

Another embodiment of the present disclosure provides for methods oftransforming from one crystal structure to another crystal structure. Anexemplary method includes: providing a TiO_(2-x)N_(x) nanocolloid thathas an anatase crystal structure, wherein x is about 0.005 to 0.25;mixing the TiO_(2-x)N_(x) nanocolloid with a metal hydrate compound at atemperature of less than about 20 to 30° C.; and irradiating theinteraction of the mixture of TiO_(2-x)N_(x) nanocolloid and the metalhydrate compound with a laser energy of greater than 120 mW; andtransforming the anatase crystal structure to a rutile crystalstructure.

Other systems, methods, features, and advantages of the presentdisclosure will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within these descriptions, be within the scope ofthe present disclosure, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1A is a low resolution transmission electron micrograph (TEM) imageof titanium oxynitride nanostructures. FIG. 1B is a high resolution (HR)TEM image showing the polycrystailine character and lattice planes ofthe sample. The HR TEM image corresponds to an anatase crystal structureconfirmed by the x-ray powder diffraction pattern shown in the inset.

FIG. 2 includes (a) a reflection spectrum for Degussa P25™ TiO₂ whosespectrum rises sharply at 380 nanometers (nm), (b) a reflection spectrumof titanium oxynitride nanoparticles (3-11 nm) whose spectrum risessharply at 450 nm, and (c) a reflection spectrum of titanium oxynitridepartially agglomerated nanoparticles whose spectrum rises sharply at 550nm.

FIG. 3 includes (a) an infrared spectrum for triethylamine showing aclear C-H stretch region, and (b) an infrared spectrum of titaniumoxynitride nanoparticies (3-11 nm) corresponding to the yellow titaniumoxynitride crystallites whose reflection spectrum rises sharply at 450nm.

FIG. 4 is an XPS spectrum for untreated titanium dioxide nanoparticlesand titanium oxynitride nanoparticles. The nitrogen peak, which ispresent in the titanium oxynitride nanoparticle sample, but not in theuntreated titanium dioxide, is considerably more pronounced for thepalladium treated titanium oxynitride nanoparticles.

FIG. 5A is an XRD powder pattern for untreated titanium dioxide powders.FIG. 5B is an XRD powder pattern for titanium oxynitride partiallyagglomerated nanoparticles corresponding with the sharply risingreflectance spectrum at 550 nm. While the XRD patterns in FIGS. 5A and5B are indicative of the anatase phase, the broad XRD pattern forpalladium treated titanium oxynitride may be attributed to a structuraltransformation.

FIG. 6A is a TEM of a palladium metal impregnated titanium oxynitridenanostructure. FIG. 6B is a TEM micrograph of a dark brown-black crystalphase accompanying the palladium impregnated nitride nanostructures. Thedark crystallites are associated with a structural transformation (e.g.,the analog of octahedrite in titanium dioxide).

FIG. 7A is a graph illustrating the photodegradation of methylene bluein water at pH 7 and at about 390 nm. FIG. 7B is a graph illustratingthe photodegredation of methylene blue in water at pH 7 and at about 540nm.

FIG. 8A illustrates Raman spectrum of untreated anatase TiO₂nano-powder, while FIG. 8B illustrates the Raman spectrum of nitridizedTiO₂ nano-colloid. The dashed line represents the fitted data and solidline represents the data. The spectrum in FIG. 8B is broader because thenanoparticles used are smaller.

FIG. 9A illustrates Raman spectra of the TiO₂ nanocolloid prepared withvarious concentrations of Co using CoCl₂, while FIG. 9B illustratesRaman spectra of the TiO₂ nanocolloid prepared with variousconcentrations of Co using Co(NO₃)₂. Note that the Raman signal for FIG.9A was obtained using a 1 μm spot size and a power of 25 mW or less. TheRaman signal for FIG. 9B was obtained at much higher laser powers (e.g.,150 mW) and is laser induced.

FIG. 10 illustrates Raman spectra of TiO_(2-x)N_(x) nano-colloid forvarious Co concentrations using CoCl₂.

FIG. 11 illustrates and compares Raman spectra of the initialTiO_(2-x)N_(x) and Co-doped TiO_(2-x)N_(x) nanocolloids (laser-induced).

FIG. 12 illustrates the Raman spectrum of Ni doped TiO₂ nanocolloid atpowers less than 20 mW.

FIG. 13 illustrates the laser-induced Raman spectrum and fit forTiO_(2-x)N_(x) doped with CoCl₂. The vibrations at 388 cm⁻¹ and 690 cm⁻¹have been assigned to a cobalt oxide site similar to that in Co₃O₄(spinels).

DETAILED DESCRIPTION

Embodiments of the present disclosure include methods of treating TiO₂nanocolloids, methods of treating TiO_(2-x)N_(x) nanocolloids, andmethods of transforming the crystal structure from the anatase crystalstructure to the rutile crystal structure for each of the TiO₂nanocolloids and TiO_(2-x)N_(x) nanocolloids. Initially in eachinstance, the TiO₂ nanocolloids and the TiO_(2-x)N_(x) nanocolloids havean anatase crystal structure. The TiO₂ nanocolloids and theTiO_(2-x)N_(x) nanocolloids are each mixed with a metal hexahydratecompound. The crystal structure of the TiO₂ nanocolloids and theTiO_(2-x)N_(x) nanocolloids are each changed from the anatase crystalstructure to the rutile crystal structure at conditions substantiallydifferent than current techniques. In particular, the transformationsare carried out at temperatures significantly less than that typicallyassociated with the anatase to rutile transformation, which occursstoichiometrically and requires a temperature of about 850° C. for atime period of about 12 hours. The methods of the present disclosure areadvantageous for at least the reasons that the transformation from theanatase crystal structure to the rutile crystal structure in TiO₂nanocolloids and the TiO_(2-x)N_(x) nanocolloids are conducted at muchlower temperatures and/or significantly faster times than previousmethods.

In addition, embodiments of the present disclosure provide foroxynitride nanoparticles having the following formula: M_(x)O_(y)N_(z)where M is a metal, a metalloid, a lanthanide, or an actinide; O isoxygen; N is nitrogen, and where x can range from about 1 to 3; y isabout 0.5 to less than 5, and z is about 0.001 to 0.5, about 0.001 to0.2, and about 0.001 to 0.1.

Another embodiment of the present disclosure provides for methods ofpreparation of M_(x)O_(y)N_(z) nanoparticles. An exemplary method ofpreparing M_(x)O_(y)N_(z) nanoparticles includes mixing at least onetype of oxide nanoparticle (described below) with at least one alkylamine at room temperature until the reaction between the oxidenanoparticle and alkyl amines is substantially complete (e.g., typicallyless than 60 seconds). The result is the formation of M_(x)O_(y)N_(z)nanoparticles. Subsequently, the M_(x)O_(y)N_(z) nanoparticles can bedried in a vacuum and stored for use in the future.

In addition, another embodiment provides for oxynitride nanoparticleshaving the following formula: M1_(x1)M2_(x2)O_(y)N_(z), where M1 and M2can be a metal, a metalloid, a lanthanides, an actinides, orcombinations thereof; x1 and x2 are in the range from about I to 3; y isabout 0.5 to less than 5; and z is about 0.001 to 0.5. Anotherembodiment provides for methods of preparing M1_(x1)M2_(x2)O_(y)N_(z)nanoparticles. The method is similar to the method described above inregard to M_(x)O_(y)N_(z) nanoparticles and will be described in moredetail below.

Another embodiment of the present disclosure provides forM_(x)O_(y)N_(z) nanoparticles having a catalytic metal(M_(x)O_(y)N_(z)[M_(CAT)]) disposed thereon and/or therein. Arepresentative method of the preparation of M_(x)O_(y)N_(z)[M_(CAT)]nanoparticles includes mixing at least one type of oxide nanoparticlewith at least one alkyl amine and a catalytic metal compound until thereaction between the oxide nanoparticle, alkyl amines, and catalyticmetal compound is substantially complete (e.g., typically less than 60seconds). The result is the formation of M_(x)O_(y)N_(x)[M_(CAT)]nanoparticles. Subsequently, the M_(x)O_(y)N_(r)[M_(CAT)] particles canbe vacuum dried and stored for use in the future.

In addition, another embodiment provides for M1_(x1)M2_(x2)O_(y)N_(z)nanoparticles having catalytic metal (M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)]disposed thereon and/or therein and methods of formation thereof. Themethod is similar to the method described above in regard toM_(x)O_(y)N_(z)[M_(CAT)] nanoparticles and will be discussed in moredetail below.

Other embodiments of the present disclosure include the use of one ormore types of M_(x)O_(y)N_(z), M_(x)O_(y)N_(z)[M_(CAT)],M1_(x1)M2_(x2)O_(y)N_(z), and/or M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)]nanoparticles in catalysts, for photocatalytic reactors, inphotocatalytic supports, in solar panel energy systems, and in pigments.

For example, one or more types of M_(x)O_(y)N_(z),M_(x)O_(y)N_(z)[M_(CAT)], M1_(1x)M2_(x2)O_(y)N_(z), and/orM1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles can be used as aphotocatalyst for converting water into hydrogen and oxygen. Inaddition, one or more types of M_(x)O_(y)N_(z),M_(x)O_(y)N_(z)[M_(CAT)], M1_(x1)M2_(x2)O_(y)N_(z), and/orM1_(x1)M2_(X2)O_(y)N_(z)[M_(CAT)] nanoparticles can be used in thephotodegradation of organic molecules present in polluted water and air.

In particular, TiO_(2-x)N_(x) and/or TiO_(2-x)N_(x)[Pd] nanoparticlescan be used in photocatalytic reactors, solar cells, and pigments. Forexample, the TiO_(2-x)N_(x) and/or TiO_(2-x)N_(x)[Pd] nanoparticles canbe incorporated into porous silicon structures (e.g., micro/nanoporousstructures) and act as a catalyst, a photocatalyst, or an electrodematerial.

M_(x)O_(y)N_(z) Nanoparticles

Embodiments of the M_(x)O_(y)N_(z) nanoparticles include, but are notlimited to, the following formulas: MO_(1-s)N_(s) (where s is in therange of about 0.001 to 0.5), MO_(2-t)N_(t) (where t is in the range ofabout 0.001 to 0.5), M₂O_(3-u)N_(u) (where u is in the range of about0.001 to 0.5), M₃O_(4-v)N_(v) (where v is in the range of about 0.001 to0.5), and M₂O_(5-w)N_(w) (where w is in the range of about 0.001 to0.5). In addition, the M_(x)O_(y)N_(z) nanoparticles are less than about40 nanometers (nm) in diameter, in the range of about 8 nm to 40 nm, inthe range of about 15 nm to 35 nm, and in the range of about 20 nm to30nm.

As indicated above, M includes the transition metals, the metalloids,the lanthanides, and the actinides. More specifically, M includes, butis not limited to, titanium (Ti), zirconium (Zr), hafnium (Hf), tin(Sn), nickel (Ni), cobalt (Co), zinc (Zn), tantalum (Ta), silicon (Si),silver (Ag), iridium (Ir), platinum (Pt), palladium (Pd), gold (Au), orcombinations thereof. In particular, M can be Ti, Zr, Hf, Si, and Snand, preferably, M is Ti.

Embodiments of the M_(x)O_(y)N_(z) nanoparticles include, but are notlimited to, TiO_(2-t)N_(t) nanoparticles, ZrO_(2-t)N_(t) nanoparticles,HfO_(2-t)N_(t) nanoparticles, SiO_(2-t)N_(t) nanoparticles, andSnO_(2-t N) _(t) nanoparticles.

Embodiments of the M_(x)O_(y)N_(z) nanoparticles have the characteristicthat they are able to absorb radiation (e.g., light) in the range ofabout 350 run to 2000 nm, about 500 nm to 2000 nm, about 540 nm to 2000nm, about 450 nm to 800 nm, about 500 nm to 800 nm, about 540 nm to 800nm, and about 540 nm to 560 nm. Preferably, the M_(x)O_(y)N_(z)nanoparticles absorb radiation at about 550 nm, the peak of the solarspectrum.

In general, the M_(x)O_(y)N_(z) nanoparticles may maintain their crystalstructure upon nitridation. However, some embodiments of theM_(x)O_(y)N₂ nanoparticles may experience crystal phase transformation.In particular, nitridation of anatase TiO₂ nanoparticles do not appearto experience phase transformation whereas nitridation of TiO₂nanoparticles in the presence of PdCl₂ results in a structuraltransformation (e.g., transformation from the anatase crystal phase to acomplex mixed structural phase).

Methods of Making M_(x)O_(y)N_(z) Nanoparticles

Embodiments of the present disclosure also include methods of preparingM_(x)O_(y)N_(z) nanoparticles. An embodiment of a representative methodincludes mixing at room temperature at least one type of oxidenanoparticle (M_(h)O_(i) nanoparticles (where h is in the range of about1 to 3 and i is in the range of about 1 to 5)) with an excess of asolution having at least one type of alkyl amine. The solution can alsocontain hydrazine and/or ammonia.

In general, the M_(h)O_(i) nanoparticles have a diameter of less thanabout 40 nm, in some embodiments less than about 30 nm. The M_(h)O_(i)nanoparticles may be in several forms. In particular, the M_(h)O_(i)nanoparticles can be suspended in a colloidal solution of one or moretypes of M_(h)O_(i) nanoparticles; a gel of one or more types ofM_(h)O_(i) nanoparticles; one or more types of M_(h)O_(i) nanoparticles;or combinations thereof.

For M_(h)O_(i) nanoparticles, M includes the transition metals, themetalloids, the lanthanides, and the actinides. More specifically, Mincludes, but is not limited to, Ti, Zr, Hf, Sn, Ni,.Co, Zn, Pb, Mo, V,Al, Nb, Ta, Si, Ag, Ir, Pt, Pd, Au, or combinations thereof. Inparticular, M can be Ti, Zr, Hf, Si, and Sn and, preferably, M is Ti.

The alkyl amine can include, but is not limited to, compounds having theformula of N(R₁)(R₇)(R₃). R₁, R₂, and R₃ can each be selected fromgroups such as, but not limited to, a methyl group, an ethyl group, apropyl group, and a butyl group. The preferred alkyl amine istriethylamine. In general, an excess amount (based on the quantity ofM_(h)O_(i) nanoparticles) of alkyl amine is included in the mixture toensure complete reaction of the M_(h)O_(i) nanoparticles. However, it iscontemplated and within the scope of this disclosure that amounts lessthan an excess of alkyl amine can be included in the mixture to produceM_(x)O_(y)N_(z) nanoparticles.

Subsequent to providing M_(h)O_(i) nanoparticles and the alkyl amine,the M_(h)O_(i) nanoparticles and the alkyl amine can be mixed in acontainer, preferably a closed glass container with a magnetic stirringrod. Alternatively, the mixture can be mixed by shaking the containerwith a machine or by hand. The M_(h)O_(i) nanoparticles and the alkylamine are mixed until reaction between them is substantially complete,which may be indicated by an exothermic reaction (e.g., heat release)and/or by a color change of the mixture. The reaction typically takesless than 60 seconds and, preferably, less than 10 seconds to formM_(x)O_(y)N_(z) nanoparticles.

After the reaction between the M_(h)O_(i) nanoparticle and the alkylamine is complete, the mixture is allowed to air dry. Subsequently, themixture is dried under a vacuum (about 5×10⁻² torr) for less thanapproximately 12 hours. The M_(x)O_(y)N_(z) nanoparticles are typicallycolored (e.g., a yellow to orange/red color for titanium oxynitrideparticles).

M_(x)O_(y)N_(z) [M_(CAT)] Nanoparticles

M_(x)O_(y)N_(z) [M_(CAT)] nanoparticles include M_(x)O_(y)N_(z)nanoparticles (as described above in reference to M_(x)O_(y)N_(z)nanoparticles) having one or more catalytic metals (M_(CAT)) disposedthereon and/or incorporated therein. The M_(CAT) can be a metal such as,but not limited to, palladium (Pd), silver (Ag), ruthenium (Rh),platinum (Pt), cobalt (Co), copper (Cu), or iron (Fe).

It appears that the M_(CAT) can be incorporated onto (or impregnates)the M_(x)O_(y)N_(z) nanoparticles structure, and/or the M_(CAT) can bedispensed on the surface of the M_(x)O_(y)N_(z) nanoparticles to formM_(x)O_(y)N_(z) [M_(CAT)] nanoparticles. In addition, the M_(CAT) canpromote the alteration of the crystal structure of the M_(x)O_(y)N_(z)nanoparticles. In one embodiment, the crystal structure of the TiO₂nanoparticles changes from an anatase crystal structure to a complexstructural mixture, which may include octahedrite crystal(e.g.,TiO_(2-t)N_(t)[Pd] (where t is in the range of about 0.001 to0.5)). This transformation of structure takes place upon reaction of theTiO₂ nanoparticles with an alkyl amine and PdC1₂.

Embodiments of the M_(x)O_(y)N_(z) [M_(CAT)] nanoparticles may have thecharacteristic that they are able to absorb radiation (e.g., light) inthe range of about 350 nm to about 2000 nm, about 500 nm to 2000 nm,about 540 nm to 2000 nm, about 450 nm to about 800 nm, about 500 nm to800 nm, about 540 nm to 300 nm, and about 540 nm to 560 nm. Preferably,the M_(x)O_(y)N_(z) [M_(CAT)] nanoparticles may absorb radiation atabout 550 nm, the peak of the solar spectrum.

Methods of Making M_(x)O_(y)N_(7r) [M_(PAT)I Nanoparticles

Another embodiment of the present disclosure includes preparingM_(x)O_(y)N_(z)[M_(CAT)] nanoparticles by mixing at room temperature atleast one type of M_(h)O_(i) nanoparticle, a catalytic metal compound,and an excess of a solution having at least one type of alkyl amine.After the reaction between the at least one type of M_(h)O_(i)nanoparticle, the catalytic metal compound, and the at least one type ofalkyl amine is substantially complete, the mixture is allowed to airdry. Subsequently, the mixture is dried under a vacuum (about 5×10⁻²torr) for less than 12 hours. The resulting M_(x)O_(y)N_(z)[M_(CAT)]nanoparticles are typically colored (e.g., a brown-black color fortitanium oxynitride particles having Pd metal disposed thereon(TiO_(2-x)N_(x)[Pd])).

The catalytic metal compound can include compounds such as, but notlimited to, palladium chloride (PdCl₂), silver chloride (AgCl),ruthenium chloride (RhCl₄), platinum chloride (PtCl₂), cobalt chloride(COCl₂), copper chloride (CuCl₂), and iron chloride (FeCl₂). Notintending to be bound by theory, it appears that the catalytic metalcompound may serve one or more purposes. For example, the catalyticmetal compound catalyzes the reaction of the M_(h)O_(i) nanoparticlesand the alkyl amine, as well as the increased uptake of nitrogen to formM_(x)O_(y)N_(z) [M_(CAT)] nanoparticles.

M1_(x1)M2_(x2)O_(y)N_(z) Nanoparticles

Another embodiment of the present disclosure provides for oxynitridenanoparticles having the following formula: M1_(x1)M2_(x2)O_(y)N_(z),where x1 and x2 are in the range from about 1 to 3, y is about 0.5 toless than 5, and z is about 0.001 to less than 5.

For the M1_(x1)M2_(x2)O_(y)N_(z) nanoparticles, M1 and M2 can includethe transition metals, the metalloids, the lanthanides, the actinides,of combinations thereof. More specifically, M1 and M2 can include, butare not limited to, Ti, Zr, Hf, Sn, Ni, Co, Zn, Pb, Mo, V, Al, Nb, Ta,Si, Ag, Ir, Pt, Pd, Au, or combinations thereof. In particular, M1 andM2 can be Ti, Zr, Hf, Si, and Sn, or combinations thereof.

Embodiments of the M1_(x1)M2_(x2)O_(y)N_(z) nanoparticles may have thecharacteristic that they are able to absorb radiation (e.g., light) inthe range of about 350 nm to 2000 nm, about 500 nm to 2000 nm, about 540nm to 2000 nm, about 450 nm to 800 nm, about 500 nm to 800 nm, about 540nm to 800 nm, and about 540 nm to 560 nm. Preferably, theM1_(x1)M2_(x2)O_(y)N_(z) nanoparticles may absorb radiation at about 550nm, the peak of the solar spectrum.

Methods of Making M1_(x1)M2_(x2)O_(y)N_(z) Nanoparticles

Embodiments of the present disclosure also include methods of preparingM1_(x1)M2_(x2)O_(y)N_(z) nanoparticles. An embodiment of arepresentative method includes mixing at room temperature two types ofoxide nanoparticles (M_(h)O_(i) nanoparticles (where h is in the rangeof about 1 to 3 and i is in the range of about 1 to 5)) with an excessof a solution having at least one type of alkyl amine. The solution canalso contain hydrazine and/or ammonia.

Subsequently, the two types of M_(h)O_(i) nanoparticles and the alkylamine can be mixed in a container, preferably a closed glass container,with a magnetic stirring rod. Alternatively, the mixture can be mixed byshaking the container with a machine or by hand. The two types ofM_(h)O_(i) nanoparticles and the alkyl amine are mixed until thereaction is substantially complete, which maybe indicated by anexothermic reaction (e.g., heat release) and/or by a color change of themixture. After the reaction between the two types M_(h)O_(i)nanoparticles and the alkyl amine is complete, the mixture is allowed toair dry. Subsequently, the mixture is dried under a vacuum (about 5×10⁻²torr) for less than 12 hours.

Another representative method includes mixing a mixed oxide nanoparticlehaving the formula M1_(h1)M2_(h2)O_(i) (where h1 and h2 can range fromabout 1 to 3 and i is in the range of about 1 to 5) with an excess of asolution having at least one type of alkyl amine. The solution can alsocontain hydrazine and/or ammonia.

Subsequently, the M1_(h1)M2_(h2)O_(i) nanoparticles and the alkyl aminecan be mixed in a container, preferably a closed glass container, with amagnetic stirring rod. Alternatively, the mixture can be mixed byshaking the container with a machine or by hand. The M1_(h1)M2_(h2)O_(i)nanoparticles and the alkyl amine are mixed until the reaction issubstantially complete, which maybe indicated by an exothermic reaction(e.g., heat release) and/or by a color change of the mixture. After thereaction of the M1_(h1)M2_(h2)O_(i) nanoparticles and the alkyl amine iscomplete, the mixture is allowed to air dry. Subsequently, the mixtureis dried under a vacuum (about 5×10⁻² torr) for less than 12 hours.

M, M1, M2, and the alkyl amines correspond to the descriptions providedabove and will not be described here in any more detail.

M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] Nanoparticles

M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles includeM1_(x1)M2_(x2)O_(y)N_(z) nanoparticles (as described above in referenceto M1_(h1)M2_(h2)O_(i) nanoparticles) having one or more catalyticmetals (M_(CAT)) disposed thereon and/or incorporated therein. Asdescribed above, the M_(CAT) can be a metal such as, but not limited to,Pd, Ag, Rh, Pt, Co, Cu, or Fe.

Embodiments of the M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles mayhave the characteristic that they are able to absorb radiation (e.g.,light) in the range of about 350 nm to 2000 nm, about 500 nm to 2000 nm,about 540 nm to 2000 nm, about 450 nm to 800 nm, about 540 nm to 800 nm,about 500 nm to 800 nm, and about 540 nm to 560 nm. Preferably, theM1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles may absorb radiation atabout 550 nm, the peak of the solar spectrum.

Methods of Making M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] Nanoparticles

Another embodiment of the present disclosure includes preparingM1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles. A representative methodincludes mixing at room temperature two types of M_(h)O_(i)nanoparticles with a catalytic metal compound and an excess of asolution having at least one type of alkyl amine. The solution can alsocontain hydrazine and/or ammonia.

Subsequently, the two types of M_(h)O_(i) nanoparticles, the catalyticmetal compound, and the alkyl amine can be mixed in a container,preferably a closed glass container, with a magnetic stirring rod.Alternatively, the mixture can be mixed by shaking the container with amachine, or by hand. The two types of M_(h)O_(i) nanoparticles, thecatalytic metal compound, and the alkyl amine are mixed until thereaction is substantially complete, which maybe indicated by anexothermic reaction (e.g., heat release) and/or by a color change of themixture. After the reaction between the two types M_(h)O_(i)nanoparticles, the catalytic metal compound, and the alkyl amine iscomplete, the mixture is allowed to air dry. Subsequently, the mixtureis dried under a vacuum (about 5×10⁻² torr) for less than 12 hours.

Another representative method includes mixing M1_(h1)M2_(h2)O_(i) with acatalytic metal compound, and an excess of a solution having at leastone type of alkyl amine. The solution can also contain hydrazine and/orammonia. Subsequently, the M1_(h1)M2_(h2)O_(i) nanoparticles, thecatalytic metal compound, and the alkyl amine can be mixed in acontainer, preferably a closed glass container, with a magnetic stirringrod. Alternatively, the mixture can be mixed by shaking the containerwith a machine or by hand. The M1_(h1)M2_(h2)O_(i) nanoparticies, thecatalytic metal compound, and the alkyl amine are mixed until thereaction is substantially complete, which maybe indicated by anexothermic reaction (e.g., heat release) and/or by a color change of themixture. After the reaction of the M1_(h1)M2_(h2)O_(i) nanoparticies,the catalytic metal compound, and the alkyl amine is complete, themixture is allowed to air dry. Subsequently, the mixture is dried undera vacuum (about 5×10⁻² torr) for less than 12 hours.

M, M1, M2, M_(CAT), the catalytic metal compound, and the alkyl aminescorrespond to the descriptions provided above and will not be describedhere in any more detail.

TiO₂ Nanocolloid Crystal Phase Transformation

Embodiments of the present disclosure include methods of treating TiO₂nanocolloids having an anatase crystal structure with a metal hydratecompound (e.g., metal halide hexahydrate compounds) and directlytransforming the crystal structure of the TiO₂ nanocolloids from theanatase crystal structure to the rutile crystal structure. The methodsare carried out at temperatures significantly less than currenttechniques, which can approach 850° C. for the stoichiometricconversion, and at much faster times than this conversion, which takesabout 12 hours. In another embodiment, the method includes treating TiO₂nanocolloids having an anatase crystal structure with a metal hydratecompound (e.g., metal nitrate hexahydrate compounds) and transformingthe crystal structure of the TiO₂ nanocolloids from the anatase crystalstructure to the rutile crystal structure via a laser-inducedtransformation (e.g., greater than about 120-150 mW). Additional detailsregarding the TiO₂ nanocolloid crystal phase transformation as well asthe laser-induced transformation are described below and in Example 3.

In general, the TiO₂ nanocolloids having an anatase crystal structureare mixed with a metal hydrate compound (e.g., a metal hexahydratecompound) at a temperature of less than 600° C. (e.g., roomtemperature). The crystal structure transforms from anatase to rutile inless than 60 minutes (e.g., 5 minutes), while at a temperature of lessthan 600° C. (e.g., room temperature). Embodiments of the method producea resultant transformation of the TiO₂ nanocolloid from the anatase to arutile crystal structure. In another embodiment, the metal replaces aportion of the Ti in the nanocolloid. For example, cobalt (Co) replacessome of the Ti in the nanocolloid (See Example 3 for additionaldetails).

The TiO₂ nanocolloids are initially anatase TiO₂ nanoparticlecrystallites. The TiO₂ nanocolloids are synthesized using the sol-geltechnique to form exclusively the anatase structure. The resultingliquidous form of the nanocolloid solution is treated with a metalhexahydrate (e.g., cobalt hexahydrate or nickel hexahydrate), forexample. The TiO₂ nanocolloids can have a width (e.g., the longestdimension of a non-spherical nanoparticle or the diameter of asubstantially spherical nanoparticle) of about 6 to 10 nm, and can beagglomerated into larger particles.

The metal hydrate compound can include, but is not limited to, metalhexahydrate compounds and other metal hydrate compounds where the metalhas a lower secondary hydrate coordination (e.g., magnetic transitionmetal hydrate compounds, where the coordination of hydrate depends uponthe magnetic transition metal). The metal hexahydrate compound caninclude, but is not limited to, magnetic transition metal hexahydrates.The concentration of the metal hydrate compound that is mixed with theTiO₂ nanocolloids is about 3 to 45 mole %.

In an embodiment for direct transformation from anatase to rutile, themetal hexahydrate compound can include, but is not limited to, metalhalide hexahydrate compounds. In particular, the halide is chlorine. Themetal hexahydrate compound can include, but is not limited to, cobaltmetal hexahydrate compounds and nickel metal hexahydrate compounds. Inparticular, the cobalt metal hexahydrate compound is a cobalt chloridehexahydrate compound, while the nickel metal hexahydrate compound is anickel metal chloride hexahydrate compound. In an embodiment, theconcentration of the cobalt chloride hexahydrate compound that is mixedwith the TiO₂ nanocolloids is about 3 to 40 mole %. In an embodiment,the concentration of the nickel chloride hexahydrate compound that ismixed with the TiO₂ nanocolloids is about 3 to 40 mole %.

In an embodiment for transformation from anatase to rutile vialaser-induced transformation, the metal hexahydrate compound caninclude, but is not limited to, metal nitrate hexahydrate compounds. Themetal hexahydrate compound can include, but is not limited to, cobaltmetal hexahydrate compounds and nickel metal hexahydrate compounds. Inparticular, the cobalt metal hexahydrate compound is a cobalt nitratehexahydrate compound, while the nickel metal hexahydrate compound is anickel metal nitrate hexahydrate compound. In an embodiment, theconcentration of the cobalt nitrate hexahydrate compound that is mixedwith the TiO₂ nanocolloids is about 5 to 45 mole %. In an embodiment,the concentration of the nickel nitrate hexahydrate compound that ismixed with the TiO₂ nanocolloids is about 5 to 45 mole %.

As mentioned above, embodiments of the method include mixing the TiO₂nanocolloid with a metal hexahydrate compound at a temperature of lessthan about 600° C., less than about 550° C., less than about 500° C.,less than about 450° C., less than about 400° C., less than about 350°C., than about 300° C., less than about 250° C., less than about 200°C., less than about 150° C., less than about 100° C., less than about75° C., less than about 50° C., less than about 40° C., and less thanabout 30° C. In an embodiment, the temperature is about 20 to 30° C. orabout 25° C.

Embodiments of the method include transforming from the anatase crystalstructure to the rutile crystal structure in less than 60 minutes, inless than 50 minutes, in less than 40 minutes, in less than 30 minutes,in less than 20 minutes, in less than 10 minutes, in less than 5minutes, and in less than 3 minutes. In an embodiment, thetransformation from the anatase crystal structure to the rutile crystalstructure occurs in less than 5 minutes. It should be noted that thetransformation from the anatase crystal structure to the rutile crystalstructure occurs at the temperatures noted above.

TiO_(2-x)N_(x) Nanocolloid Crystal Phase Transformation

Embodiments of the present disclosure include methods of treatingTiO_(2-x)N_(x) nanocolloids having an anatase crystal structure with ametal hydrate compound (e.g., metal hexahydrate compound) and, inconcert with laser illumination (e.g., 514.5 nm), transforming (e.g.,laser-induced transformation at greater than about 120-150 mW of power)the crystal structure of the TiO_(2-x)N_(x) nanocolloids from theanatase crystal structure to the rutile crystal structure. It should benoted that x is about 0.005 to 0.25. Additional details regardingTiO_(2-x)N_(x) nanocolloid crystal phase transformation are described inExample 3.

In general, the TiO_(2-x)N_(x) nanocolloids having an anatase crystalstructure are mixed with a metal hydrate compound at a temperature ofless than 600° C. (e.g., room temperature). The crystal structuretransforms via laser-induced transformation from anatase to rutile inless than 60 minutes (e.g., 5 minutes) at a temperature of less than600° C. (e.g., room temperature) upon exposure to the radiation energy(e.g., a laser light energy). Embodiments of the method produce aTiO_(2-x)N_(x) nanocolloid and/or a TiO_(2-x)N_(x) nanocolloid/metalcomplex having a rutile crystal structure. In another embodiment, themetal replaces a portion of the Ti in the complex.

The TiO_(2-x)N_(x) nanocolloids can be formed using methods as describedherein. The TiO_(2-x)N_(x) nanocolloids can include anataseTiO_(2-x)N_(x) nanoparticle crystallites. The TiO_(2-x)N_(x)nanocolloids can be in the form of a slurry formed via the amination ofa sol-gel generated TiO₂ liquidous solution. The TiO₂ solution that isinitially slightly opaque is transformed to an off-white, nearly opaqueviscous fluid, which can be condensed into a gel; when dried in vacuum,it produces yellow crystallites. The TiO_(2-x)N_(x) nanocolloids canhave a width (e.g., the longest dimension of a non-sphericalnanoparticle or the diameter of a substantially spherical nanoparticle)of about 6 to 10 nm, which can be agglomerated to form largerstructures.

The metal hydrate compound can include, but is not limited to,transition metal hydrates and magnetic transition metal hydrates. Inaddition, the metal hydrate compound can include, but is not limited to,metal hexahydrate compounds and other metal hydrate compounds where themetal has a lower secondary hydrate coordination (e.g., transition metalhydrate compounds and magnetic transition metal hydrate compounds, wherethe coordination of hydrate depends upon the magnetic transition metal).The metal hexahydrate compound can include, but is not limited to,transition metal hexahydrates. In an embodiment, the metal hexahydratecompound can include, but is not limited to, magnetic transition metalhexahydrates. The concentration of the metal hydrate compound that ismixed with the TiO_(2-x)N_(x) nanocolloids is about 3 to 40 mole %.

In an embodiment for transformation from anatase to rutile vialaser-induced transformation, the metal hexahydrate compound caninclude, but is not limited to, metal halide hexahydrate compounds andmetal nitrate hexahydrate compounds. In particular, the halide ischlorine. The metal hexahydrate compound can include, but is not limitedto, cobalt metal hexahydrate compounds and nickel metal hexahydratecompounds. In particular, the cobalt metal hexahydrate compound is acobalt chloride hexahydrate compound. In an embodiment, theconcentration of the cobalt chloride hexahydrate compound that is mixedwith the TiO₂ nanocolloids is about 3 to 40 mole %.

Embodiments of the method include mixing the TiO_(2-x)N_(x) nanocolloidswith a metal hexahydrate compound and treating with a laser (e.g., atgreater than about 120-150 mW) at temperatures as described in regard tothe TiO₂ nanocolloid methods. In an embodiment, the temperature is about20 to 30° C. or about 25° C.

Embodiments of the method include the laser-aided transformation fromthe anatase crystal structure to the rutile crystal structure in a timeframe as described above in regard to TiO₂ nanocolloid methods. In anembodiment, the laser-aided transformation from the anatase crystalstructure to the rutile crystal structure occurs in less than 5 minutes.It should be noted that the transformation from the anatase crystalstructure to the rutile crystal structure occurs at the temperaturesnoted above.

Embodiments of the method include irradiating the mixture ofTiO_(2-x)N_(x) nanocolloids and the metal hexahydrate compound. Theirradiation source can include, but is not limited to, a laser source.In an embodiment, the laser source can include, but is not limited to,an argon ion, a krypton ion, or a pulsed nitrogen laser source.

EXAMPLE 1

The following is a non-limiting illustrative example of an embodiment ofthe present disclosure. This example is not intended to limit the scopeof any embodiment of the present disclosure, but rather is intended toprovide specific experimental conditions and results. Therefore, oneskilled in the art would understand that many experimental conditionscan be modified, but it is intended that these modifications are withinthe scope of the embodiments of the present disclosure.

This example discusses the formation of TiO_(2-x)N_(x) nanoparticles onthe order of seconds at room temperature employing the directnitridation of TiO₂ nanostructures using alkyl ammonium compounds.Photocatalytically active TiO_(2-x)N_(x) particles were produced, whichabsorb well into the visible region (e.g., from about 350 nm to 2000nm). The TiO_(2-x)N_(x) particles are (i) stable, (ii) inexpensive,(iii) have a conduction band minimum that is higher than the H₂/H₂Ocouple (described above), and (iv) can absorb most of the photons of thesolar spectrum.

TiO₂ nanoparticles prepared by the controlled hydrolysis of titanium(IV) tetraisopropoxide in water under deaerated conditions can vary insize between 3 and 11 nm and forms a nearly transparent colloidalsolution, which is stable for extended periods under refrigeration.Extended exposure to air at room temperature or controlled heating at50° C. produces a mild agglomeration of the TiO₂ nanoparticles andresults in the formation of a virtually opaque gel. Both the initialTiO₂ nanoparticle colloidal solution and the agglomerated gel solutionare treated with an excess of triethylamine. The mixture is mixed with aTeflon®-coated magnetic stirrer (or by shaking) in a small closed glasscontainer. A reaction is found to take place readily between the TiO₂nanoparticle colloidal solution and the triethylamine, which appears tobe complete within several seconds following heat release and theformation of a yellowish, partially opaque, mixture. Upon drying andexposure to a vacuum of 5×10⁻² Torr for several hours, the treated,initially transparent, nanoparticle solution forms deep yellowcrystallites whose transmission electron micrograph (TEM), highresolution (HR) TEM, and electron diffraction patterns are illustratedin FIGS. 1A and 1B. The treated, partially agglomerated, nanoparticlegel is found to form orange to orange-red crystallites. XRD and HR TEMsdemonstrate that both the treated nanoparticle structures corresponddominantly to the anatase crystalline form of TiO_(2-x)N_(x), as do theoriginal TiO₂ nanoparticle crystallites.

FIG. 2 compares (a) the optical reflectance spectrum for Degussa P25™TiO₂ (reported at an average size of 30 nm), onsetting sharply at about380 nm; (b) the reflectance spectrum for TiO_(2-x)N_(x) nanoparticles(3-11 nm), rising sharply at 450 nm; and (c) the corresponding spectrumfor TiO_(2-x)N_(x) partially agglomerated nanoparticles, rising sharplyat 550 nm.

In addition, PdC1₂ was introduced into another nitriding amine-TiO₂mixture. The corresponding transmission electron micrograph andphotoelectron spectra obtained for TiO_(2-x)N_(x) nanoparticles (3-11nm) with palladium incorporation (about 1 μg added to the nitridingsolution), demonstrated not only the effects of an increased nitrogenuptake but also the impregnation of the TiO_(2-x)N_(x) structure withreduced Pd nanostructures (TiO_(2-x)N_(x)[Pd]). Furthermore, it wasobserved that the TiO_(2-x)N_(x) anatase crystal structure was alsoconverted to alternate crystal phase forms (possibly the octahedriteform) for some of the TiO_(2-x)N_(x) nanoparticles. TheTiO_(2-x)N_(x)[Pd] agglomerated nanoparticles, which are brown-black incolor, absorb radiation at wavelengths in the range of about 450 nm to2000 nm.

In contrast to the nanoparticle activity, no measurable reaction or heatrelease is observed as either distinct rutile or anatase TiO₂micropowders are treated directly with an excess of triethylamine. Thetreatment of DeGussa P25™ “nanopowders” (mean distribution of about 30nm) results in a much slower reactive process, over several hours, whichappears to decant the smaller nanoparticles from the material. Thetreatment forms a pale brown crystalline form, which yields a complexreflectance spectrum. The TiO₂ nanoparticle solutions also interactstrongly with hydrazine and to a lesser extent with an ammoniumhydroxide (NH₃) solution. However, the reaction with triethylamine isfound to be facile at room temperature, leading to nitrogenincorporation into the TiO₂ lattice to form TiO_(2-x)N_(x) nanoparticleswhen the direct nitridation process is carried out at a nanometer scale.

The infrared spectra depicted in FIG. 3 demonstrate another aspect ofthe nitridation process. Specifically, there is no evidence forhydrocarbon incorporation in the final doped TiO₂ product. The IRspectrum shown in FIG. 3( a) corresponds to that for the trialkylamine,demonstrating, among other features, the clear alkyl C—H stretch region.In contrast, the IR spectrum shown in FIG. 3( b), corresponding to theyellow TiO_(2-x)N_(x) nanocrystallites (yielding a reflectance spectrumof about 450 nm) pressed into a KBr pellet, shows virtually no infraredspectra especially in the C—H stretch region. This indicates virtuallyno residual organic incorporation after the air and vacuum dryingprocesses have been performed on the nitrided TiO₂ nanoparticles. Thisobservation is consistent both with photoelectron (XPS) and X-raydiffraction (XRD) studies.

XPS studies detect the presence of nitrogen not only at the surface, butalso incorporated into the TiO_(2-x)N_(x) nanoparticle agglomerates overa range from about 2.5 to 5.1 atomic % and increasing from about 7.5 to17.1 atomic % for the Pd treated samples. XPS spectra for TiO₂ andTiO_(2-x)N_(x) are compared in FIG. 4. The nitrogen concentrationsindicated above should be compared to less than 1 atomic % for a virginTiO₂ powder. The XRD data taken for TiO₂ (FIG. 5A) and the nitridedpartially agglomerated TiO₂ gel solution (FIG. 5B) show the effects of aclear expansion of the “a” lattice parameter, due presumably to nitrogenincorporation. XRD is a sensitive tool for determining whether thenitrogen dopants are actually incorporated on interstitial lattice sitesof the TiO₂ particles or are merely adsorbed at the surface. Nitrogendoping was found to lead to a measurable increase of the interplanarspacings in the agglomerated TiO₂ particles and peak broadening, whichcan be attributed to the strain fields of interstitially dissolvednitrogen atoms and also the breaking at the TiO₂ lattice structure. Theanalysis of the XRD patterns demonstrates the presence of a dominantanatase phase in both the untreated TiO₂ nanoparticles and the dopedsamples (Table 1 below) for either the nitrided TiO₂ nanoparticles (3-11nm) or partially agglomerated TiO₂ nanoparticle samples. In this case noevidence for any degree of conversion from the anatase to the rutilestructure was found.

TABLE 1 A, c, Sample Phase a, (A) standard c(A) standard None Rutile4.5986 .0006 2.9634 .0006 Processed Anatase 3.7862 .0004 9.5070 .0011TiO₂ Orange TiC > 2 Anatase 3.7942 00.32 9.4676 .0075

However, the XRD pattern, observed for the nitrided TiO₂ nanoparticles(3-11 nm) treated with palladium is broad and complex and demonstratesnot only the formation of the Pd crystallites but also an apparentconversion from the anatase structure to an alternate phase, which maybe, in part, the analog of the tetragonal octahedrite structure of TiO₂.The TEM micrographs of FIGS. 6A and 6B demonstrate both the impregnationof the TiO_(2-x)N_(x) structure with smaller “reduced” palladiumnanoparticles, as well as the formation of a significant additionalalternate structure. The Pd treated samples appear black in color,indicating that they absorb well into the near infrared region.

Photocatalytic activity was evaluated by measuring the decomposition ofmethylene blue at 390 and 540 nm, respectively, using a Clark MXR™ 2001femtosecond laser producing a 1 khz pulse train of 120 femtosecondpulses. The laser output was used to pump either an optical parametricamplifier to obtain tunable wavelengths in the visible spectrumincluding 540 nm or a second harmonic generation crystal to produce 390nm.

FIG. 7A illustrates the photodegradation observed at 390 nm formethylene blue in water at ph 7. The data for the nitrided TiO₂nanoparticle samples, as well as the palladium treated TiO₂nanoparticles referred to above, are consistent with a notably enhancedactivity for the TiO_(2-x)N_(x) nanoparticle constituencies at 390 nm.FIG. 7B illustrates the photodegradation observed at 540 nm in which thepartially agglomerated nitrided TiO_(2-x)N_(x) and palladium treatedTiO₂ nanoparticle samples still display a notable activity, whereas theactivity for TiO₂ nanoparticle is considerably muted. In contrast, atwavelengths below 350 nm, the activity of both the TiO₂ nanoparticlesand nitrided TiO₂ nanoparticle samples is comparable. Thus, nitridedTiO_(2-x)N_(x) nanoparticle samples, which can be generated in severalseconds at room temperature, are catalytically active at considerablylonger wavelengths than TiO₂ nanoparticles.

These results demonstrate that by forming and adjusting an initial TiO₂nanoparticle size distribution and mode of nanoparticle treatment, it ispossible to tune and extend the absorption of a doped TiO_(2-x)N_(x)sample well into the visible region. Further, these results indicatethat an important modification of a TiO₂ photocalalyst can be madeconsiderably simpler and more efficient by extension to the nanometerregime. The current process can produce submicrometer agglomerates of adesired visible light-absorbing TiO_(2-x)N_(x) nanoparticle via a roomtemperature procedure, which otherwise is highly inefficient, if notinoperative, at the micron scale.

EXAMPLE 2

The following is a non-limiting illustrative example of an embodiment ofthe present disclosure. This example is not intended to limit the scopeof any embodiment of the present disclosure, but rather is intended toprovide specific experimental conditions and results. Therefore, oneskilled in the art would understand that many experimental conditionscan be modified, but it is intended that these modifications are withinthe scope of the embodiments of the present disclosure.

This example discusses the formation of ZrO_(2-x)N_(x) nanoparticles atroom temperature employing the direct nitridation of ZrO₂ nanostructuresusing alkyl ammonium compounds. An excess volume of triethyl amine wasadded to a powder of zirconium dioxide (ZrO₂) nanoparticles, and thismixture was subsequently treated with PdCl₂. The mixture was mixed witha Teflon®-coated magnetic stirrer (or shaken) in a small closed glasscontainer. A reaction was found to take place readily between the ZrO₂powder/nanoparticles and the triethylamine and appears to quicklycomplete following heat release and the formation of a yellowish,partially opaque, mixture. Upon drying and exposure to a vacuum of5×10⁻² Torr for several hours, the treated, initially white, collodial,nanoparticle solution forms pale yellow crystallites. The change incolor appears to indicate that nitrogen incorporation into the ZrO₂powder has occurred to form ZrO_(2-x)N_(x) nanostructures.

EXAMPLE 3

The following is a non-limiting illustrative example of an embodiment ofthe present disclosure. This example is not intended to limit the scopeof any embodiment of the present disclosure, but rather is intended toprovide specific experimental conditions and results. Therefore, oneskilled in the art would understand that many experimental conditionscan be modified, but it is intended that these modifications are withinthe scope of the embodiments of the present disclosure.

The TiO₂ nanoparticle crystallites and the TiO_(2-x)N_(x), nanoparticlecrystallites are formed in a manner as described above. Each of the TiO₂nanoparticle crystallites and the TiO_(2-x)N_(x), nanoparticlecrystallites have been treated with Co⁺² and Ni⁺² hexahydrates. Inparticular, the Co hexahydrates include cobalt chloride hexahydrate(also referred to as CoCl₂) and cobalt nitrate hexahydrate (alsoreferred to as Co(NO₃)₂), and the Ni hexahydrate is nickel chloridehexahydrate (also referred to as NiCl₂).

In general, the TiO₂ nanoparticle crystallites are mixed with thehexahydrate at room temperature (about 25° C.). The TiO₂ nanoparticlecrystallites are originally in the anatase form, but are converted uponinteraction with the hexahydrate to the rutile form in less than aboutfive minutes while still at about room temperature. This conversion fromanatase to rutile form is unexpected because such a stoichiometricconversion typically occurs at temperatures of the order of 850° C.after 12 hours.

In general, the TiO_(2-x)N_(x), nanoparticle crystallites are mixed withthe hexahydrate at room temperature (about 25° C.). The TiO₂nanoparticle crystallites are originally in the anatase form, but areconverted in the reaction with the hexahydrate to the rutile form uponexposure to laser light at a typical energy of about 120-150 mW in alaser spot of about 1 μm size in less than about five minutes whilestill at about room temperature (less the short exposure to the laserlight). This conversion from anatase to rutile is unexpected becausesuch conversions generally occur at temperatures approaching 850° C. for12 hour exposures.

The TiO₂ nanocolloids, nitridized TiO₂ nanocolloids subsequently Codoped, were examined by Raman spectroscopy. The μ Raman system that wasused included a Mitutoyo Microscope and a SPEX Triplemate spectrometerequipped with a CCD. The 514.5 nm line of an Ar ion laser was used asthe excitation source. The microscope had 10×, 50× and 100× objectivesfor focusing the laser light and was coupled to the spectrometer througha fiber optic bundle. The light from the microscope was filtered by a514.5 nm notch filter. The positions of the Raman lines in a givenspectrum were calibrated against the 546.0 nm emission line from afluorescent light source.

FIGS. 8A and 8B illustrate examples of the Raman spectrum of untreatedas well as triethylamine-treated TiO₂ nanostructured powders. Theresults indicate that the untreated TiO₂ nanopowder includes only theanatase crystal structure, as identified by the three Raman lines near400 cm⁻¹, 515 cm⁻¹ and 635 cm⁻¹, shown in FIG. 8A. The Raman spectrumfor a triethylamine-treated TiO₂ nanocolloid is shown in FIG. 8B. Afternitridation, the nanocolloid remained anatase, but an additional featureappears near 550 cm⁻¹. This feature has been attributed to the presenceof the non-stoichiometric titanium oxynitride. A background luminescenceis also present in the nitridized sample and thus it is also included inthe fit, as shown in FIG. 8B.

The Raman spectra of the CoCl₂ treated TiO₂ nano-colloid, for variousinitial Co concentrations, are shown in FIG. 9A, and the Raman spectrafor Co(NO₃)₂-treated TiO₂ are shown in FIG. 9B. Note that for the CoCl₂treated samples, the Raman signal intensity drops as a function ofincreasing Co content. In the case of Co(NO₃)₂ treated samples, however,the opposite is true, and the Raman signal strength, which islaser-induced, increases with increasing Co content.

Similar results can also be seen in the case of CoCl₂ doping of thenitrided TiO₂ nanocolloid, TiO_(2-x)N_(x), as shown in FIG. 10. TheRaman signal strength in this case decreases with decreasing Coconcentration, which is similar to the results noted for Co(NO₃)₂treated TiO₂, but it is opposite to the behavior of the Co(Cl)₂ treatedTiO₂ nanocolloid.

Another interesting result is that although the initial TiO₂ andTiO_(2-x)N_(x) nanocolloids are exclusively of the anatase crystalstructure, (shown in FIGS. 8A and 8B), the Co doped material hastransformed almost completely, exhibiting the more stable rutilestructure (vibrations near 235 cm⁻¹, 440 cm⁻¹, and 605 cm⁻¹) depicted inblack in FIG. 11. In this figure, the initial TiO_(2-x)N_(x) nanocolloidstructure, which is anatase, is plotted along with the Raman spectrum.

It should be noted that this structural transformation is not unique todoping with Co. In fact, a similar structural change has also been notedin Ni doped (NiCl₂) TiO₂ nanocolloids, as demonstrated in FIG. 12. Inthis case, the crystal structure, as determined from the Raman spectrum,also corresponds at least in part to the rutile phase, althoughadditional phase transformations are indicated.

In addition to the characteristic rutile Raman lines evident in theCo—TiO₂, there are several more Raman lines that are not characteristicof the rutile or the anatase phase of TiO₂. These can be seen in FIGS.8A, 8B, 9A, and 9B and in FIG. 13, which is the Raman spectrum of aTiO₂—Co(NO₃)₂ nanocolloid. In this case, the lines at 388 cm⁻¹ and 690cm⁻¹ do not correspond to a structural phase of TiO₂. However, it hasbeen reported previously that the vibrations of spinel (Co₃0₄), withwhich are associated it's tetrahedaral Co⁺² sites, result in a 383 cm⁻¹line, while the Alg phonon mode of spinel has been reported at 691 cm⁻¹.It is thus suggested that these phonon modes result from CoO sites inthe TiO₂ lattice that are similar to those sites in Co₃O₄, most likelyformed during the solution and laser treatments of the TiO₂ andTiO_(2-x)N_(x) nanocolloids. The vibrations at 388 cm⁻¹ and 690 cm⁻¹have been assigned to a cobalt oxide site similar to that in Co₃O₄.

It should be emphasized that the above-described embodiments of thepresent disclosure, particularly, any “preferred” embodiments, aremerely possible examples of implementations, merely set forth for aclear understanding of the principles of the disclosure. Many variationsand modifications may be made to the above-described embodiment(s) ofthe disclosure without departing substantially from the spirit andprinciples of the disclosure. All such modifications and variations areintended to be included herein within the scope of this disclosure andthe present disclosure and protected by the following claims.

1. A method of transforming from one crystal structure to another crystal structure, comprising: providing a TiO₂ nanocolloid that has an anatase crystal structure; mixing the TiO₂ nanocolloid with a metal hexahydrate compound at a temperature of less than about 600° C., wherein the metal hexahydrate compound is selected from a group consisting of: a cobalt chloride hexahydrate compound, a cobalt nitrate hexahydrate compound, and a nickel chloride hexahydrate compound; and transforming the anatase crystal structure to a rutile crystal structure in less than 60 minutes and at a temperature of less than about 600° C.
 2. A method of transforming from one crystal structure to another crystal structure, comprising: providing a TiO₂ nanocolloid that has an anatase crystal structure; mixing the TiO₂ nanocolloid with a metal hydrate compound at a temperature of about 20 to 30° C.; and transforming the anatase crystal structure to a rutile crystal structure in less than 5 minutes and at a temperature of about 20 to 30° C.
 3. The method of claim 2, wherein the metal hydrate compound comprises a transition metal hydrate compound.
 4. The method of claim 2, wherein the metal hydrate compound comprises a magnetic transition metal hydrate compound.
 5. The method of claim 2, wherein the metal hydrate compound comprises a cobalt hexahydrate compound.
 6. The method of claim 5, wherein the cobalt hexahydrate compound is a cobalt chloride hexahydrate compound.
 7. The method of claim 2, wherein the metal hydrate compound comprises a nickel hexahydrate compound.
 8. The method of claim 7, wherein the nickel hexahydrate compound comprises a nickel chloride hexahydrate compound.
 9. The method of claim 2, wherein transforming occurs at about 25° C.
 10. The method of claim 2, further comprising forming a TiO₂ nanocolloid/metal complex, wherein the TiO₂ nanocolloid/metal complex is a TiO₂ nanocolloid/Co complex, wherein Co replaces at least one Ti in the rutile crystal structure.
 11. The method of claim 2, wherein the metal hydrate compound comprises a transition metal chloride hexahydrate compound.
 12. A method of transforming from one crystal structure to another crystal structure, comprising: providing a TiO_(2-x)N_(x) nanocolloid that has an anatase crystal structure, wherein x is about 0.005 to 0.25; mixing the TiO_(2-x)N_(x) nanocolloid with a metal hexahydrate compound at a temperature of less than about 600° C., wherein the metal hexahydrate compound is selected from a group consisting of: a cobalt chloride hexahydrate compound, a cobalt nitrate hexahydrate compound, and a nickel chloride hexahydrate compound; irradiating the interaction of the mixture of the TiO_(2-x)N_(x) nanocolloid and the metal hexahydrate compound with a laser energy of greater than 120 mW; and transforming the anatase crystal structure to a rutile crystal structure.
 13. A method of transforming from one crystal structure to another crystal structure, comprising: providing a TiO_(2-x)N_(x) nanocolloid that has an anatase crystal structure, wherein x is about 0.005 to 0.25; mixing the TiO_(2-x)N_(x) nanocolloid with a metal hydrate compound at a temperature of about 20 to 30° C.; and irradiating the interaction of the mixture of TiO_(2-x)N_(x) nanocolloid and the metal hydrate compound with a laser energy of greater than 120 mW; and transforming the anatase crystal structure to a rutile crystal structure.
 14. The method of claim 13, wherein the metal hydrate compound comprises a transition metal hydrate compound.
 15. The method of claim 14, wherein the metal hydrate compound is selected from a transition metal chloride hydrate compound and a transition metal nitrate hydrate compound.
 16. The method of claim 13, wherein the metal hydrate compound comprises a magnetic transition metal hydrate compound.
 17. The method of claim 16, wherein the metal hydrate compound is selected from a magnetic transition metal chloride hydrate compound and a magnetic transition metal nitrate hydrate compound.
 18. The method of claim 13, wherein the metal hydrate compound comprises a cobalt hexahydrate compound.
 19. The method of claim 18, wherein the cobalt hexahydrate compound is selected from cobalt chloride hexahydrate compound and cobalt nitrate hexahydrate compound.
 20. The method of claim 13, wherein transforming occurs at about 25° C. 